1. Technical Field
The present disclosure relates to an organic light-emitting device, and more particularly, to an organic light-emitting device that provides increased lifespan and decreased driving voltage, and an organic-light-emitting display using the same.
2. Discussion of the Related Art
In the information age, the field of displays visually expressing signals related to electrical information has rapidly developed. To satisfy such a trend, various flat display devices having excellent performance, such as thinness, light weight, and low power consumption, have been researched as a substitute for a conventional cathode ray tube (CRT) display device. Examples of flat display devices include liquid crystal displays (LCDs), plasma display panels (PDPs), field emission displays (FEDs), organic light-emitting diode (OLED) displays, etc. The OLED display requires no separate light source, and has been considered to be competitive in achieving compactness and good color reproduction.
The organic light-emitting display includes a plurality of sub-pixels, and each sub-pixel includes an organic light-emitting device. An OLED includes an anode, a cathode, and a plurality of organic layers between the anode and the cathode. The organic light-emitting device emits light when a current is applied between the anode and the cathode.
At least one layer of the organic layers between the anode and the cathode is an organic light-emitting layer. Holes and electrons from the anode and cathode are injected into the organic light-emitting layer and are combined with each other in the organic light-emitting layer, thus generating excitons. When the generated excitons are changed from an excited state to a ground state, the organic light-emitting diode emits light. For example, a basic structure of the organic light-emitting diode includes an anode and a cathode, and a hole injection layer, a hole transport layer, an organic light-emitting layer, an electron transport layer and electron injection layer sequentially stacked from the anode, between the anode and the cathode.
Meanwhile, it is preferable that the electrons and the holes are contained in the organic light-emitting layer for high emission efficiency. For this, it has been suggested to provide an electron blocking layer (EBL) between the hole transport layer and the organic light-emitting layer, such that the electron blocking layer prevents the electrons from leaking in the organic light-emitting layer when the current is applied between the anode and the cathode.
However, some electrons from the organic light-emitting layer may escape to the hole transport layer, even though the electron blocking layer is provided. Thus, the moved electrons remain in the hole transport layer, and cause deterioration of the hole transport layer and higher driving voltage. Accordingly, there is a difficulty to realize a particular extended lifetime for the device.
Also, the electron blocking layer requires a broad bandgap for smoothly transporting holes and blocking electrons, but known materials used for the electron blocking layer have high LUMO (Lowest Unoccupied Molecular Orbital) and high HOMO (Highest Occupied Molecular Orbital), and thus have a narrow bandgap. Therefore, the organic light-emitting device having the electron blocking layer of known material has problems, such as insufficient hole injection/transportation into the light-emitting layer and high driving voltage.